This study examines the underlying mechanism that connects career social support with employability through a survey of 392 Chinese college students. The results showed that career social support had a positive effect on career adaptation and employability of college students, and career adaptation mediated the association between career social support and employability. Furthermore, proactive personality was found to play a moderating role in linking career adaptation and employability. More specifically, higher levels of a proactive personality strengthen the enhancing effect of career adaptation on the employability of college students. Therefore, there was a moderated mediation effect between career social support and employability of college students.